package org.bouncycastle.crypto.macs;

import java.util.Hashtable;

import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.ExtendedDigest;
import org.bouncycastle.crypto.Mac;
import org.bouncycastle.crypto.params.KeyParameter;

/**
 * HMAC implementation based on RFC2104
 * 
 * H(K XOR opad, H(K XOR ipad, text))
 */
@SuppressWarnings({ "rawtypes", "unchecked" })
public class HMac implements Mac {
    private final static byte IPAD = (byte) 0x36;
    private final static byte OPAD = (byte) 0x5C;

    private Digest digest;
    private int digestSize;
    private int blockLength;

    private byte[] inputPad;
    private byte[] outputPad;

    private static Hashtable blockLengths;

    static {
        blockLengths = new Hashtable();

        blockLengths.put("GOST3411", Integer.valueOf(32));

        blockLengths.put("MD2", Integer.valueOf(16));
        blockLengths.put("MD4", Integer.valueOf(64));
        blockLengths.put("MD5", Integer.valueOf(64));

        blockLengths.put("RIPEMD128", Integer.valueOf(64));
        blockLengths.put("RIPEMD160", Integer.valueOf(64));

        blockLengths.put("SHA-1", Integer.valueOf(64));
        blockLengths.put("SHA-224", Integer.valueOf(64));
        blockLengths.put("SHA-256", Integer.valueOf(64));
        blockLengths.put("SHA-384", Integer.valueOf(128));
        blockLengths.put("SHA-512", Integer.valueOf(128));

        blockLengths.put("Tiger", Integer.valueOf(64));
        blockLengths.put("Whirlpool", Integer.valueOf(64));
    }

    private static int getByteLength(Digest digest) {
        if (digest instanceof ExtendedDigest) {
            return ((ExtendedDigest) digest).getByteLength();
        }

        Integer b = (Integer) blockLengths.get(digest.getAlgorithmName());

        if (b == null) {
            throw new IllegalArgumentException("unknown digest passed: "
                    + digest.getAlgorithmName());
        }

        return b.intValue();
    }

    /**
     * Base constructor for one of the standard digest algorithms that the
     * byteLength of the algorithm is know for.
     * 
     * @param digest
     *            the digest.
     */
    public HMac(Digest digest) {
        this(digest, getByteLength(digest));
    }

    private HMac(Digest digest, int byteLength) {
        this.digest = digest;
        digestSize = digest.getDigestSize();

        this.blockLength = byteLength;

        inputPad = new byte[blockLength];
        outputPad = new byte[blockLength];
    }

    public String getAlgorithmName() {
        return digest.getAlgorithmName() + "/HMAC";
    }

    public Digest getUnderlyingDigest() {
        return digest;
    }

    public void init(CipherParameters params) {
        digest.reset();

        byte[] key = ((KeyParameter) params).getKey();

        if (key.length > blockLength) {
            digest.update(key, 0, key.length);
            digest.doFinal(inputPad, 0);
            for (int i = digestSize; i < inputPad.length; i++) {
                inputPad[i] = 0;
            }
        } else {
            System.arraycopy(key, 0, inputPad, 0, key.length);
            for (int i = key.length; i < inputPad.length; i++) {
                inputPad[i] = 0;
            }
        }

        outputPad = new byte[inputPad.length];
        System.arraycopy(inputPad, 0, outputPad, 0, inputPad.length);

        for (int i = 0; i < inputPad.length; i++) {
            inputPad[i] ^= IPAD;
        }

        for (int i = 0; i < outputPad.length; i++) {
            outputPad[i] ^= OPAD;
        }

        digest.update(inputPad, 0, inputPad.length);
    }

    public int getMacSize() {
        return digestSize;
    }

    public void update(byte in) {
        digest.update(in);
    }

    public void update(byte[] in, int inOff, int len) {
        digest.update(in, inOff, len);
    }

    public int doFinal(byte[] out, int outOff) {
        byte[] tmp = new byte[digestSize];
        digest.doFinal(tmp, 0);

        digest.update(outputPad, 0, outputPad.length);
        digest.update(tmp, 0, tmp.length);

        int len = digest.doFinal(out, outOff);

        reset();

        return len;
    }

    /**
     * Reset the mac generator.
     */
    public void reset() {
        /*
         * reset the underlying digest.
         */
        digest.reset();

        /*
         * reinitialize the digest.
         */
        digest.update(inputPad, 0, inputPad.length);
    }
}
